Problem: $\dfrac{6}{8} - \dfrac{4}{8} = {?}$
$ = {\dfrac{6 \times 1}{8 \times 1}} - {\dfrac{4 \times 1}{8 \times 1}} $ $ = {\dfrac{6}{8}} - {\dfrac{4}{8}} $ $ = \dfrac{{6} - {4}}{8} $ $ = \dfrac{2}{8}$